CalDav is supported on the iPhone 3.0 version. You can now enter items into Google Calendar on your PC and it will update automatically on your iPhone without syncing the device. It also works the other way around. Add an item to your iPhone calendar and it will show up on Google Calendar.

You can also see your Toodledo tasks on Gcal and Gmail (yes, the iCal is 1-way, but you can use the gadget to edit tasks on Gcal), and unlike Google Tasks, Toodledo has more than just list names. Honestly, I don't know how anyone really uses Google Tasks. They are just about as limited as possible.

I would love to centralize everything into a single time management system. Toodledo is great as a task manager (contexts, tags, and iPhone application) and Google Calendar as event manager (Google Tasks lacks the ability to set due time and context(to events) which are a limitation). If events could have assigned contexts, you could apply the 2-minute rule to events that are set in the calendar scheduled in the future or in the past. For me that`d be integrated GTD (there won`t be difference between events or a tasks since both are actionable items).